When creating large directories or large databases, it is sometimes necessary, primarily for scaling purposes, to partition the data so that each server only holds a subset of the data. The data is front ended by a proxy or chaining function, so that the aggregate of all data is presented as a single directory or database. This partitioning may occur for a variety of directory technologies, including, but not limited to, directories accessed via Lightweight Directory Access Protocol (LDAP), directories implementing the X.500 standards, Home Location Registry (HLR) directories used by telephone service providers, and others. This partitioning may also occur for a variety of database technologies, including, but not limited to, relational databases, indexed flat file databases, and object oriented databases. For example, Tivoli® Directory Server allows for a directory with 180 million entries. To add additional read capacity, the directory server can create additional replicas. But this does not help to provide additional write capacity because each change roust be propagated to every copy. Therefore the directory server partitions the date so that each server holds only a subset. The 180 million entries may be split into 6 partitions, each with 30 million entries.
For a directory, the partitions can be made by creating a hash of the naming attribute for a given object, and allocating the entries to 6 hash buckets. Each of the hash buckets define a partition of the data stored on a separate server. A database may be partitioned in a similar way, for example by hashing on a primary key. A proxy is implemented to route operation requests (search, add, delete, modify, etc.) to each of the partitions so that the partitions appear as one large directory.
As the amount of data grows, the original number of partitions becomes inadequate. In the above example, the 180 million entries might grow over time to 300 million entries. To support the levels of load, 10 partitions of the data are required instead of 6. To increase the number of partitions, the system is stopped. While the system is stopped, the data is partitioned into 10 partitions. After the 10 partitions are created, the system is restarted. While the system is stopped, however, access to the data is interrupted.